1. Field of the Invention
The present invention relates generally to a wireless communication system, and more particularly, to a method and apparatus for multi-cell cooperative transmission in a wireless communication system.
2. Description of the Related Art
When adjacent cells use the same frequency in a cellular communication environment, severe interference occurs at a cell edge. Techniques that have been proposed to reduce inter-cell interference and increase the capacity of a cell edge. Among them, 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) and Institute of Electrical and Electronics Engineers (IEEE) IEEE 802.16e/16m support Inter-Cell Interference Coordination (ICIC). ICIC is a technology for reducing inter-cell interference by controlling transmission power per frequency resource over a long term, considering the traffic and interference of Mobile Stations (MSs) within each cell. Although ICIC can reduce interference with MSs at a cell edge by preventing neighbor cells from transmitting signals in specific frequency resources or controlling the neighbor cells to transmit signals in the frequency resources with reduced transmission power, ICIC has limitations in increasing capacity due to reduction of inter-cell interference only through resource allocation and transmission power control.
Compared to ICIC, Coordinated Multi-Point (CoMP) transmission/reception or multi-cell Multiple Input Multiple Output (MIMO) coordinates neighbor cells with one another according to the instantaneous channel and traffic state of a cell-edge MS.
One of the CoMP schemes, Coordinated Scheduling/Coordinated Beamforming (CS/CB) CoMP increases the capacity of a cell-edge MS by selecting, when a plurality of Base Stations (BSs) communicate with MSs through beamforming, antenna beamforming for each of the BSs in such a manner that a signal from a serving BS is strongest and interference signals from neighbor BSs are weakest. CS/CB CoMP cooperative BSs transmit data only to their MSs, not to the MSs of neighbor cooperative cells. Another CoMP scheme, Joint Processing (JP) CoMP increases the capacity of a cell-edge MS by enabling a plurality of neighbor BSs to transmit the same information to the cell-edge MS almost simultaneously. Additionally, a plurality of BSs may simultaneously transmit user signals to a plurality of MSs in order to increase overall cell capacity. Therefore, JP CoMP cooperative BSs transmit data to MSs of neighbor cooperative cells as well as to their MSs.
Despite the advantage of an increased cell-edge and average cell capacity compared to ICIC, CoMP has deficiencies in that a large amount of information should be received through a backhaul, for BS cooperation, and scheduling for resource allocation and CoMP signal processing computation is complex.